1. Field of the Invention
The present invention concerns a method employing the acquisition of magnetic resonance data to track an item, such as a catheter, using a transmit array system of a magnetic resonance data acquisition unit. More specifically, the method concerns tracking the rotational orientation and position of the item, and separating the item from the surrounding anatomy in the resulting magnetic resonance image or spectroscopic data.
2. Description of the Prior Art
A precise and fast localization of interventional devices is a necessity to perform minimally invasive operations. Generally, X-ray imaging is used for these operations due to almost perfect instrument visualization and determination of catheter orientation. X-ray imaging, however, cannot provide soft tissue contrast, and ionizing radiation is exposed to patients as well as staff.
On the other hand, MRI is a non-ionizing imaging modality that offers impressive soft tissue contrast as compared to X-ray imaging. One of the main challenging problems in MR-guided interventions is the difficulty in real-time detection and tracking of the interventional devices, such as catheters, guidewires, and biopsy needles. Various techniques have been developed for identification of interventional devices. Although, the passive and active catheter tracking methods have distinct advantages, the passive tracking methods have reliability problems (Kochli V D, McKinnon G C, Hofmann E, Vonschulthess G K. Vascular Interventions Guided by Ultrafast Mr-Imaging—Evaluation of Different Materials. Magnetic Resonance in Medicine 1994; 31(3):309-314), and device handling in the active tracking techniques is not easy. There are also hybrid methods and they make use of an inductively coupled RF (ICRF) (Quick H H, Zenge M O, Kuehl H, Kaiser G, Aker S, Massing S, Bosk S, Ladd M E. Interventional magnetic resonance angiography with no strings attached: Wireless active catheter visualization. Magnetic Resonance in Medicine 2005; 53(2):446-455; Celik H, Uluturk A, Tali T, Atalar E. A catheter tracking method using reverse polarization for MR-guided interventions. Magn Reson Med 2007; 58(6):1224-1231) coil. Even though many researchers introduced solutions for tracking problem of interventional devices such as biopsy needles and catheters, rotational orientation of a catheter is a relatively untouched subject.
In all of the applications and methods mentioned above, conventional imaging systems have been used. On the other hand transmit array systems have recently been introduced for experimental studies. Yet these studies are mostly concentrated on understanding the working principles, exploring the capabilities of the system, and homogenizing the high frequency B1 fields (Katscher U, Börnert P, Leussler C, van den Brink J S. Transmit SENSE. Magnetic Resonance in Medicine 2003; 49(1):144-150; Adriany G, Van de Moortele P F, Wiesinger F, Moeller S, Strupp J P, Andersen P, Snyder C, Zhang X, Chen W, Pruessmann K P, Boesiger P, Vaughan T, U{hacek over (g)}urbil K. Transmit and receive transmission line arrays for 7 Tesla parallel imaging. Magnetic Resonance in Medicine 2005; 53(2):434-445. Pinkerton R G, Near J P, Barberi E A, Menon R S, Bartha R. Transceive surface coil array for MRI of the human prostate at 4T. Magnetic Resonance in Medicine 2007; 57(2):455-458). Although usage of transmit array systems has been limited, the use of transmit array system was recently introduced in our previous study to obtain reverse polarization during transmission.